Cathode ray tube



Nov.20', 1934. T, N'AKAJIMAEAL 1,981,322

CATHODE RAY TUBE Filed Nov. 16, l 19:52

' INVENIQRS.

ATTORNEYS.

Patented Nov. 20, 1934 UNITED STATES CATHODE RAY TUBE Tomomasa Nakajima and Kenjiro Takayanagi,

Hamamatsu, Japan Application November 16, 1932, Serial No. 642,970

4 Claims.

Our invention relates to an improvement in'a cathode ray tube particularly adapted foruse in connection with the television receiving systemas fully disclosed and claimed in our copending U. S.

5 application; Serial No. 574,160 filed Nov. 10, 1931.

In the said copending application, since the deflecting elements of the cathode ray tube are en-, ergized with a saw-tooth shaped deflecting current the direct current component corresponding to the mean value of the saw-tooth wave must always pass through the deflecting coils so that the image on the fluorescent plate is initially deflected in one direction and cannot reproduce the imag at the centre of the fluorescent plate.

v Hence, the principal object of our invention is to provide a cathode ray tube whereby the dis-.

placement of the reproduced image from the central position of its fluorescent plate may be positively obviated.

A further object of our invention is to provide a cathode ray tube having means whereby the initial deflection of the linear axis of the electron passage of the tube due to the mean value of the saw-tooth shaped current or voltage may be easily neutralized.

For a better understandingof our invention, together with other and further objects thereof,

reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in theappended claims. Fig. 1 of the accompanying drawing is a diagrammatic view of a cathode ray tube provided with deflecting elements according tothis invention; Fig. 2 illustrates a cross section of the cathode ray tube shown in Fig. 1; Fig. 3 shows a preferable connection for the coils shown in Fig. 2 and Fig. 4 illustrates a modification of the neutralizing device shown in Figs. 2 and 3.

Now referring to Fig. 1 of the accompanying drawing, 1 represents a. cathode ray tube comprising an anode 2, a grid 3 and a filament 4, the

electron passage of which is to be controlled. 5

is a focussing coil to concentrate the light spot on the fluorescent plate 6 of the cathode ray tube 1.

According to this invention two pairs of crossed deflecting coils 77' and 8-8 are arranged in crossed positions at the outside of the tube 1 adjacentto the fluorescent plate 6 and considerably apart from the focussing coil 5. The defleeting coils 77' and 88' are connectedrespectively to the last amplifiers 9 and 10 of the independent saw tooth current generating devices which producehigh and low deflecting fre quencies respectively as fully disclosed in our above mentioned cope'nding application. 9

Other pairs of coils l1-ll' and 12l2' whic are referred hereinafter as neutralizing coils, are overlapped respectively to the deflecting coils 77' and 88 as will be seen most clearly in A preferable connection for these coils is shown in Fig. 3. In this figure, the coil pairs 77' and 11-11f are shown by the numerals 7 and 11 5 since the coils of each pair are connected in series with each other. Thus, the deflecting coil 7 is connected to the last amplifier 9 of the saw tooth deflecting current generating device and a transformer 13 is inserted in the energizing circuit for the coil 7. That is, primary winding 14 of the transformer 13 is connected in series with the coil 7 and is applied with the saw tooth voltage. The neutralizing coil 11 is connected in series with the secondary winding 15 of the transformer 13 across a battery 17 through an adjustable resistance 16. It should be noticed that the transformer 13 is not saturated by' the direct current pass- :ing through the secondary winding 15 from the battery 17. Since the connection for the other deflecting coil pair 8--8' is similar to the above we have omitted its illustration.

The operation of the arrangement'shown in Figs. .1 to 3 is as follows: Assume that television signals are applied to the grid 3 of, the tube 1 5 and the anode 5, the cathode 4 and the focussing coil 5 are in normal operating condition. If the deflecting coils 7-7 and 8-8' are energized from the valves 9 and 10 respectively, the image may be reproduced upon the fluorescent plate 6 of the tube 1. 1

However, since the saw tooth current is mere unidirectional pulsating currentit corresponds to the case in which a constant direct current equal to the mean value of the saw tooth current is always supplied to the deflecting coils 7-7 and an alternating saw tooth current is superimposed thereupon. Accordingly, the image on the fluorescent plate 6 is displaced from the central position by the constant deflecting field due to the above mentioned direct current component. The deflecting coils 1lll' now operate to cancel the constant deflecting field due to said direct current component with the supply of opposing direct current from the battery 17. But the image may 5 not yet reproduce on the central position of the fluorescent plate 6, because the coils 11-11 will induce a votlage owing to the transformer action between the coils 7-7 and 11--11' overlapped one upon the other. The transformer 13 now operates to cancel this induced voltage. As above mentioned, although direct current passes through the secondary winding of the transformer 13 the transformer 13 is not saturated so that as the saw tooth current passes through'the primary winding 14 the secondarywinding 15 will induce a voltage similar in wave form to that induced by the coils 11-11. Since the transformer 13 is so designed and connected ,as to induce an equal but opposite voltage to the induced voltage of the neutralizing coil 11, the image will now be reproduced just at the centre of the fluorescent plate 6.

Fig. 4 illustrates another modification of the neutralizing device in which the direct current components of the saw tooth current passing through the deflecting coils 7-7 and 8-8 are neutralized by means of a permanent or electromagnet. A pair of pole pieces 18 andi'l8' are arranged oppositely at the outside of the tube I in a suitable angular position with respect to the crossed deflecting coils l -'7' and 88 and the legs 1919' are insulated magnetically at 20 and are energized by a permanet or electro-magnet NS. Dampers 21 and 21' may be provided for smoothing up the pulsating magnetic fluxes. It will be seen that in this. arrangement the use of the transformer 13 as shown in the previous case can be obviated.

Other minor alterations such, for instance, as shielding the deflecting coils with tin foils for obviating detrimental effects of the electrostatic field due to the deflecting coil's may bemade in many forms without departing'from the scope and spirit of our invention. I

What we claim as new and desire to secure by Letters Patent of the United States, is:

" ,1. In combination, a cathode-ray tube-comprising an anode, a grid, a filament, a focussing coil, two pairs of crossed deflecting coils and a fluorescent plate, saw tooth deflecting lurrent generating devices connected to said deflecting coils, andneutralizing means arranged adjacent to said deflecting'coils for neutralizing the magnetic field due to the direct current component of the saw tooth deflecting current passing through said deflecting coils.

2. In combination, a cathode-ray tube comprising an anode, a grid, a filament, a focussing coil, two pairs of crossed deflecting coils directly at* tached to the outside of said tube and a fluorescent plate, saw tooth current generating devices connected to said deflecting coils, neutralizing coils arranged adjacent to said deflecting coils, and a separate direct current source adapted to supply direct current to said neutralizing coils, said neutralizing coils producing equal but opposite con-' stant deflecting field to that due to the direct current component of the 'saw tooth deflecting current passing through said deflecting coils.

3. In combination; a cathode-ray tube comprising an anode, a grid, a filament, a focussing coil, two pairs of crossed deflecting coils directly attached to the outside of said tube and a fluorescent plate, saw tooth current generating devices connected to said deflecting coils, neutralizing coils overlapped on said deflecting coils for canceling a constant deflectingfleld due to the direct current component of the saw tooth deflecting current passing through said deflecting coils, a separate direct current source connected to said deflecting coils, and a transformer having a primary winding connected in series with said deto the direct current component of the sawtooth deflecting current passing through said deflecting coils which is arranged adjacent to said deflecting coils for neutralizing said constant deflecting field.

TOMOMASA NAKAJIMA. KENJIRO TAKAYANAGI. 

